The nanotexture of a surface can influence various properties of that surface such as its wettability by water and oils, its optical properties, and its chemical reactivity. Consequently, the art has sought methods and materials for controlling the nanotextures of various materials. Chemical methods such as etching processes, and physical methods such as sandblasting and other erosion processes have been utilized with success to control the microtexture of various materials. However, such methods have generally been inadequate for providing nanotextured surfaces.
The prior art, as exemplified by U.S. Pat. No. 2,306,222, has recognized that particular silane materials may be utilized to deposit a water-repellant coating onto various substrates. The coating deposited by the use of this technology is a relatively smooth coating, and various approaches have been implemented to texturize this coating so as to increase its water repellency. For example, U.S. Pat. No. 6,649,266 shows the deposition of silane coatings onto microtextured substrates to provide coatings having enhanced hydrophobicity. Another approach is described in PCT Published Application WO 2005/068399. This publication describes the use of a sol/gel chemical process for depositing a sponge-like water-repellant coating having a nanoscale roughness. Use of this technology to deposit a coating onto a surface having an additional microscale texture has been found to provide a coating with further enhanced hydrophobicity.
Despite various efforts the prior art has not been able to prepare a synthetic surface which is perfectly hydrophobic. As will be explained hereinbelow, the hydrophobic nature of a surface may be quantified by the contact angle that surface forms with a droplet of water. A perfectly hydrophobic surface has a contact angle of 180 degrees, and within the context of this disclosure, surfaces having contact angles in excess of 170 degrees are referred to as superhydrophobic. As will be further explained hereinbelow, the present invention, in one embodiment, provides for a nanotextured surface having a fibrillar coating of a water-repellant material. The fibrillar, nanotextured nature of the coating of the present invention causes the surface to be superhydrophobic.
As mentioned above, the nanotexture of surfaces can influence properties other than, or in addition to, their wettability by water. As will be further explained hereinbelow, the present invention, in other aspects, may be utilized to prepare coated surfaces which are strongly hydrophilic and/or oleophobic, or oleophilic. Also, the present invention may be utilized to prepare surfaces having controlled optical properties such as reflectivity and absorption. In further aspects of the present invention, chemical reactivity of the surfaces may be controlled by utilizing the fibrillar, nanotextured materials of the present invention. All of these embodiments and advantages of the invention will be apparent from the drawings, discussion and description which follow.